Permanent magnet brushless d-c motor with isolated sensor winding means

ABSTRACT

To provide an actual speed output signal upon operation of a permanent magnet motor having a generally trapozoidal or rectangular magnetic flux distribution, and the armature includes a plurality of pulse-energized strands, a sensor winding is placed on the armature and so located that it will pick up a harmonic of flux induced in a conductor to be cut by the rotating flux due to the rotor so that the output speed signal will be a multiple and thus readily analyzable with respect to actual speed in electronic circuitry. The sensor winding extends, preferably, in the same armature slots, or adjacent the armature windings, to be cut by all the flux derived by the rotor so that special winding locations on the armature can be avoided and the sensor winding placed on the armature in conventional positions thereof.

This application is a continuation of application Ser. No. 206,481 filedSept. 17, 1980.

The invention relates to a brushless d-c motor with a permanent magnetrotor, in which the poles, when viewed in the direction of rotation,have an approximately rectangular or trapezoidal magnetization curves.

BACKGROUND

It is known to obtain pulses from the main winding of a brushless d-cmotor when the motor operates. The frequency of the pulses isproportional to the instantaneous rotor speed and can therefore be usedfor measuring or controlling the motor speed. However, the frequency isrelatively low, to wit, p×ω_(mech), wherein p is the number of polepairs and ω_(mech) is the angular velocity of the rotor per second. Themain, or power current flowing in the winding of the motor affects thepulses in their relative phase position with respect to each other andrelative to the position of the rotor. A speed control employing thesepulses for comparing nominal or command values and actual values isundesirably affected and continuous oscillations of the rotor mayresult.

THE INVENTION

It is an object to provide a brushless d-c motor which generates pulseshaving a sufficiently high frequency proportional to the motor speed,that are, preferably, uninfluenced by the power currents flowing in themain winding of the motor, and which has low equipment requirements.

Briefly, in accordance with the invention, the stator of the motor has asensor winding thereon for picking up and coupling-out at least oneharmonic wave of the voltage induced in the stator by the rotor poles;the sensor winding is matched to the number of rotor poles which isequal to the product (2p ×L), wherein 2p is the actual number of polesof the rotor, and L is the ordinal number of the harmonic wave to bepicked up. The special harmonic fields included in the nonsinusoidallymagnetized poles induce voltages in the sensor winding in this mannercorresponding to that harmonic wave for which the sensor winding isdimensioned. The fundamental wave is substantially or completelysuppressed. Advantageously the sensor winding is located such thattransformer coupling between it and the main winding is avoided. This isachieved by a special selection of the spacial phase position betweenthe main winding and the sensor winding, or by omission of severalwinding steps and/or spacial phase shifting of part of the sensorwinding with respect to another part thereof.

A particularly simple arrangement of the sensor winding results whenseparate slots are provided for the same having a position exactlydefined relative to the main winding. For economic reasons it isadvantageous to place the sensor winding directly into the slots of themain winding, since then no additional slots are required for the sensorwinding. Transformer coupling with the main winding can still be avoidedby forming the sensor winding with two simple wave windings shiftedrelative to each other by a predetermined angle. In certain casesindividual winding steps have to be omitted.

DRAWINGS

FIG. 1 is a sectional view through a cylindrical air gap motorillustrating a first embodiment of the invention,

FIG. 2 is a sectional view through the stator of a second embodiment,

FIGS. 3A-3C are diagrams explaining FIGS. 1 and 2,

FIG. 4 is a circuit diagram explaining the invention,

FIG. 5 is a diagram of a variant of FIG. 3B showing main windingsemployed with the sheet metal stamping of FIG. 2, which windings can beadvantageously employed even independently of the sensor winding,

FIG. 6 is a plan view of the stator winding of a four pole motor withflat, or axial air gap and a sensor winding suitable for decoupling ofthe second harmonic wave,

FIG. 7 is an alternative type of the sensor winding of FIG. 6, which isparticularly suitable for flat motors having an axial stray field,

FIG. 8 is a second alternative type of the sensor winding of FIG. 6,which is also particularly suitable for flat motors having an axialstray field,

FIG. 9 is an enlarged representation of the developed magnetizationrepresented in FIG. 3A of a rotor for a cylindrical air gap,

FIG. 10A is the magnetization curve of the rotor, shown developed inFIG. 9,

FIG. 10B is the induced voltage curve in the conductor L according toFIG. 9 upon a complete revolution,

FIGS. 10C, D, E are the fundamental, the second and fourth harmonic waveof the voltage shown in FIG. 10B,

FIG. 11 is a plan view of a sensor winding for obtaining the fourthharmonic of the motor shown in FIG. 6,

FIG. 12 is a variant of FIG. 11, also for the fourth harmonic,

FIG. 13 is a sensor winding for obtaining the 15th harmonic of the motorshown in FIG. 6, to a slightly reduced scale,

FIGS. 14A-14D are diagrams illustrating the construction of a sensorwinding for obtaining the second harmonic (FIG. 14C) and the fourthharmonic (FIG. 14D), respectively, of a cylindrical air gap, externalrotor motor employing the sheet metal stamping shown in FIG. 2 and thetype of stator winding shown in FIG. 5,

FIG. 15 is the frequency spectrum resulting from analysis of the voltageμ shown in FIG. 10B, wherein the amplitude of the fundamental and of thefirst harmonic is shown only numerically,

FIGS. 16A-16E are diagrams of a four pole, three strand, three pulsebrushless d-c motor, which is formed as an external rotor motor and thestator of which has a sheet metal stamping with 24 equally distributedslots 1'-24', into which are wound the three strands of the statorwinding, and a sensor winding, for obtaining the third harmonic,separately shown in FIG. 16D.

FIGS. 17A-17E are diagrams of a two pole, three strand, three pulsebrushless d-c motor, which is formed as an external rotor motor and thestator sheet metal package of which has 6 equally distributed salientT-poles, as well as 6 auxiliary slots B, D, F, H, K and M for receivinga sensor winding for obtaining the third harmonic separately shown inFIG. 17D,

FIGS. 18A-18F are diagrams of a two pole, two strand, four pulsebrushless d-c motor which is formed as an external rotor motor and thestator sheet metal package of which has four equally distributed salientT-poles and four auxiliary slots B, D, F and H wherein the sensorwinding, separately shown in FIG. 18F, is constructed for obtaining thethird harmonic and is positioned to prevent transformer coupling withthe main winding,

FIGS. 19A-19E are diagrams of a four pole, two strand, four pulsebrushless d-c motor, which is formed as an external rotor motor and thestator sheet metal package which is identical to that of FIG. 16A andwhich has the two strands of the stator winding, as well as the sensorwinding separately shown in FIG. 19D for obtaining the third harmonic.

FIGS. 20A-20E are diagrams of a two pole, three strand, three pulsebrushless d-c motor formed as an external rotor motor, the stator sheetmetal package of which comprises three equally distributed salientpoles, as well as 15 auxiliary slots for receiving the sensor windingshown separately in FIG. 20E for obtaining the ninth harmonic,

FIG. 21 is a basic circuit diagram for operating the motors according toFIG. 16, FIG. 17 and FIG. 20, and

FIG. 22 is a basic circuit diagram for operating the motors according toFIG. 18 or FIG. 19.

FIG. 1 shows a stator sheet metal package 10 for an external rotor motorhaving a permanent magnet external rotor 11 and shown onlyschematically. This magnetization of the rotor 11 is shown in developedform in FIGS. 3A and 9. The angles spanned by the rotor are indicated inFIG. 9 for reference purposes. Two unlike monopole zones always meetdirectly, for example in FIG. 9, a north pole zone 13 and a south polezone 14, each 120° electrical long.

A galvanomagnetic sensor 16, in general a Hall-generator, is attached atthe stator, located in a position spanned by track 15 (FIG. 9). Thesouth monopole zone 14 is extended toward the left by an extension 18 of60° electrical. The north monopole zone 13 is extended toward the rightby an extension 19 by 60° electrical. The circular path or track 17 has,next to the extension 18, a zone 22 (north pole) and next to theextension 19, a zone 23 (south pole). The extension 18 and the zone 22and similarly the extension 19 and the zone 23 form a dipole zone, seeFIGS. 3A and 9. The circular paths or tracks 15 and 17 have about thesame width.

FIG. 10A shows the distribution of magnetization of the rotor 11 shownin FIG. 9. Curve B15, in solid lines, shows the magnetization curve ofpath 15 sensed by sensor 16; in addition the course of the magnetizationof path 17 is shown in dashed lines B₁₇. The curves B₁₅ and B₁₇ areidentical over all four monopole zones of rotor 11. They differ at thedipole zones 18, 22 and 19, 23. Voltage μ induced in conductor L (FIG.9) placed across the full width of the rotor 11 and upon uniformrelative motion between the rotor 11 and the conductor L is shown inFIG. 10B. An instrument 25, for example an oscilloscope, is used tomeasure the induced voltage μ. As can be seen from FIG. 10B, themonopole zone 14 induces, for example, a negative voltage 26, and themonopole zone 13, a positive voltage 27. The dipole zone formed by theextension 18 and the north pole 22 induces two identical oppositelydirected voltages, the sum of which is zero, see curve section 28 inFIG. 10B. The same is true for the extension 19 and the south pole 23which again together induce the voltage zero, which corresponds tosection 29 in FIG. 10B. To the right of this curve section 29, a curvesection 26' follows, which respective to its form is identical tosection 26.

By placing the zero point of the abscissa axis between the sections 26and 27, the voltage μ will be a complementary trigonometric function,that is f(t)=-f (-t). This function can be analyzed by Fourier analysisinto sine curves of different frequencies and amplitudes, of which FIG.10C shows the fundamental, FIG. 10D the second harmonic and FIG. 10E thefourth harmonic. The third and the sixth harmonic are approximatelyequal to zero. The FIGS. 10C to 10E only show the Fourier analysis ofthe voltage μ of FIG. 10B in its fundamental and the next few harmonics.Of course, further harmonic waves are present, and FIG. 15 shows thefull frequency spectrum, that is, the absolute values of the amplitudesof the individual harmonic waves of the voltage shown in FIG. 10B to the24th harmonic. The harmonic waves having an ordinal number 1 divisibleby three have very small amplitudes. The harmonic waves with the ordinalnumbers 2, 4, 5, 7, 8, 11 and 14 based on their relatively largeamplitudes are most suitable for evaluation. Useful signals areavailable when the slopes of the voltage shown in FIG. 10B are steep inhigh order harmonics. When the slopes are less steep, then practicallyonly the second, fourth, fifth and eighth harmonic can be evaluated.

The individual harmonic waves can be filtered in the usual way, forexample by way of band pass filters, from the voltage which is obtainedfrom the analysis device 25 (FIG. 9). This method is cumbersome and hasthe disadvantage of providing a control signal only when the motorreaches the desired speed of rotation. Starting has to be achieved in adifferent way.

In accordance with a preferred embodiment of the invention, the harmonicwaves are coupled-out, i.e. obtained so as to be available at any speed.

For purposes of explanation, consider the rotor 11 to be composed ofdifferent magnets, with each providing output waves due to the magnetsaccording to FIGS. 10C, 10D, 10E, etc. Further harmonic waves can benumerically easily calculated in the usual way. Fromthese--fictitious--waves due to the rotor magnetizations, a certain onehas to be taken and evaluated for the generation of the harmonic wavecorresponding thereto. A sensor winding is used having a distance of themagnetically active winding sections adapted tothis--fictitious--magnet, the sensor winding. Acting as a harmonicanalyzer, coupling-out primarily only the selected harmonic from thetotal of harmonic waves present.

A coreless stator can be employed for the invention and this variant isexplained in FIGS. 6 to 8. Initially, the invention will be explainedwith a stator made of slotted iron laminae and more particularly havingthe stator sheet metal package 10 shown in FIG. 1, viz., an externalrotor motor. The adaptation to an internal rotor motor requires merelyusing the cylindrical air gap 34 as a mirror and inverting rotor andstator.

The stator sheet metal page 10, FIG. 1 has eight slots to receive fourmain windings: slots 35, 36 for a main winding 37; slots 38, 39 for amain winding 40; slots 43, 44 for a main winding 45; slots 46, 47 for amain winding 48. The two slots of a main winding in each case areseparated by 120° electrical, and the individual main windings in eachcase have an angular distance of 180° electrical from each other, thatis they are as shown equally distributed around the circumference of thestator sheet metal package 10.

FIGS. 3A to 3C show the motor of FIG. 1 in developed representation. Thefigures are exploded for ease of analysis; the three components aredrawn, one beneath the other, in proper position. In operation,naturally, the position of the stator and rotor 11 constantly changerelative to each other. The main windings 37 and 45 have terminals 49,50 and are connected in series (of course, a parallel connection wouldbe possible). Similarly, the main windings 40 and 48 are connected inseries; they have its terminals 51 and 52.

FIG. 4 shows the position of the main windings in a correspondingcircuit controlled by a Hall-generator 16 placed exactly in the centerbetween the main windings 37 and 40 at the stator 10; compare FIGS. 1and 3B. The Hall-generator 16 controls two pnp-transistors 54,55 of adifferential amplifier. The transistors 54,55 serve as driving elementsfor npn output stage transistors 56,57 of which transistor 56 controlsthe current in the main windings 40 and 48 and transistor 57 controlsthe current in the main windings 40 and 48. One of the terminals of theHall-generator 16 is connected via an npn-transistor 58 serving as avariable resistor to the plus-line 59 and the other terminal via aresistor 60 to the minus-line 61. The emitters of transistors 54 and 55are connected to each other and via a common resistor 64 to bus 59. Thecollector of transistor 54 is connected via a resistor 65 to bus 61 anddirectly to the base of transistor 57. The windings 37, 45 are connectedwith their terminal 50 to the collector of transistor 56 and by terminal49 to the plus-line 59. Similarly, the windings 40,48 are connected bytheir terminal 52 to the collector of transistor 57 and with theirterminal 51 to the plus-line 59. A controlled gain amplifier 63 controlsthe conduction of transistor 58, which in the present case controls thespeed via the control current flowing into the Hall-generator 16. Asensor winding 80, responding to the second harmonic, determines actualspeed. Its construction is described below.

The operation of the circuit according to FIG. 4 is disclosed in detailin the German Patent Disclosure Document DE-OS No. 27 30 142, especiallyFIG. 2.

For receiving the sensor winding 80 to pick up the second harmonic, thestator sheet metal 10 has eight auxiliary slots 71 to 78 (FIG. 1),equally distributed around the stator circumference and having anangular distance from each other of 90° electrical. The position of allslots relative to each other is shown in FIGS. 3B and 3C to scale anddesignated with the same reference numbers. For example, it is seen thatthe auxiliary slot 71 (FIG. 3C) is located exactly in the center betweenthe main slots 35 and 36, that the auxiliary slot 72 is located exactlyin the middle between the main slots 36 and 38, etc., that is, the slotarrangement of FIG. 1 shows mirror symmetry. If one of the two statorhalves is reflected along one of the symmetry axes, for example the axis79 (FIG. 1), corresponding slots will coincide, for example 35 and 36,78 and 72, etc. The winding 80 according to FIG. 3C is a wave windingwhich is looped back into itself, that is, the winding goes fromterminal 83 through the slot 77, to the slot 76, then to the slot 75,slots 74, 73, 72 to the slot 71 and from there back to the slot 78 andthe slot 77. There the direction of the winding is reversed, and thewinding now runs in reverse direction again through slot 78, then slots71 to 76 and is then run to the outside very close to the terminal 83.If the sensor winding 80 would end at the slot 77 (terminal 84 in FIG.3C shown with dashed lines), the same harmonic of the induced voltagewould be covered, but the amplitude would only be half as large and, inparticular, such winding would also pick up pulsating stray fields,which run parallel to the rotor shaft 85 (FIG. 1).

By returning the sensor winding by the same angle of rotation of 720°electrical to the starting point, axial stray fields induce voltages ofequal and opposite magnitude in the sensor winding 80, which cancel eachother and thus do not influence the gain controlled amplifier 63 andhence the quality of the control. Naturally, for increasing the startingvoltage, the sensor winding can be wound around the stator 10 severaltimes, for example two full revolutions, and then returned by the sameangle to the starting point. The individual magnetically active sectionsof the sensor winding 80 (in the slots 71 to 78) each have an angulardistance from each other of (180° electrical: L+n×180° electrical),wherein n=0, 1, 2, . . . and L=ordinal number of the harmonic to becovered. In the present case L=2 and n=0, and therefore this angle is90° electrical. The sensor winding 80 comprises at least twomagnetically active sections. It covers the second harmonic of the rotormagnetization shown in FIG. 10D and generates therefor a measuringvoltage of twice the base frequency of the wave which can be obtainedfrom the Hall-generator 16. In addition, the zero passages havesubstantially more uniform distances compared to the zero passages ofthe Hall-voltage. In such a motor, for example, the Hall-generator 16provides four pulses per revolution, the sensor winding 80 in contrasteight pulses per revolution. In case the speed controller 63 (FIG. 4) isconstructed for the evaluation of the frequency (and not of theamplitude) of the voltage applied to it, a very accurate speed controlwith good long term stability and small temperature dependence can beachieved. Such a speed controller shown for example in the German PatentDisclosure DE-OS Document No. 26 16 044.

Example: A sheet metal package similar to FIG. 1 had a diameter of 80 mmand a thickness of 18 mm. A one wire sensor winding 80 was woundaccording to FIG. 3C. The rotor magnet 11 had an induction of 1.2 kG. Ata speed of 3600 rpm, an a-c voltage with an effective value of 0.3 voltsresulted between the terminals 83 and 86. It is a particular advantageof the described mirror symmetrical arrangement of the sensor winding 80that the induced voltages in it transformed from the main windingscancel each other and therefore do not interfere with the controlprocess.

The arrangement according to FIG. 1 has the disadvantage that a specialsheet metal stamping is required, which is only economical with largenumbers of motors. The invention, however, can also be realized withcommercial sheet metal stampings and this is shown in FIG. 2 inconnection with FIGS. 3A to 3C. The same reference numbers are used forthe same or equally acting parts as were used in the previous part ofthe description.

The sheet metal stamping 88 is also intended for a four pole motor withexternal rotor corresponding exactly to the rotor of FIG. 1 andreference is made to the description theerein. The sheet metal stamping88 has 24 slots 89 of identical shape, which, each, have a distance fromthe other of 15° mechanical=30° electrical. The individual windings arepositioned completely identically with those of FIG. 1 such that intotal eight slots remain without windings. The first main winding ishere again designated as 37, and the two slots around which it is woundhave a distance from each other of 120° electrical.

The second main winding is designated as 40, the third main winding isdesignated as 45 and the fourth main winding is designated as 48. Theyare, as shown, equally distributed around the stator circumference andare formed like the main winding 37. The magnetically active sections ofthe sensor winding 80 are designated as 80' and have, each, a distanceof 90° electrical from each other, and each lies on the bisecting linebetween two two neighboring slots of the main windings in order to avoidas described transformer coupling between the main windings and thesensor winding. The arrangement of the sensor winding 80 is identical tothat of the scheme according to FIG. 3C and the correspondingdescription is referred to.

In case it is desired to wind more copper into the sheet metal stampingaccording to FIG. 2, the loop winding 92 shown in FIG. 5 can be employedinstead of the winding pattern according to FIG. 3B. In accordance withFIG. 5, two winding sections are placed in two neighboring slots 93 and94, then two empty slots 95 and 96 follow, and then again two slots 97and 98 with windings follow. The larger angle step y₁ amounts to 120°electrical and the smaller angle step y₂ amounts to 90° electrical. Theangles are explicitly shown in FIG. 5. This embodiment of the windingresults in a better copper space factor, the induced voltage is somewhatsmoothed and a more favorable curve of the torque generated by the motorresults. It is a disadvantage of this arrangement that the sensorwinding can no longer be positioned exactly mirror symmetricallyrelative to the main windings, since in FIG. 5 the sensor winding shouldbe either in slot 95 or in slot 96. In case the slot number is doubledin a conventional metal stamping, then of course the sensor winding canalso, with the winding pattern of FIG. 5, be arranged with mirrorsymmetry, since then between the slots 95 and 96 an additional slot islocated into which the sensor winding of the corresponding section canbe placed. The main winding is then advantageously distributed over sixor eight slots, whereas, in FIG. 5, it is distributed only over 4 slots.This problem can also be solved without an increase of the number ofslots by a further step of the invention and is referred to in FIGS. 14Ato 14D.

FIG. 14A shows the 24 slots 89 of the stator sheet metal packageaccording to FIG. 2 in the usual developed way. FIG. 14B shows thearrangement of the stator winding 92 relative to the slots 89 of FIG.14A. The stator winding is identical to that of FIG. 5 and therefore ishere not described again. As explained, this arrangement results in amore favorable torque curve compared with the arrangement of FIG. 1. Theembodiment of FIG. 1 is not particularly suitable for industrialelectric motors; it is included herein primarily for explaining thebasic principle of the invention.

In the arrangement of the stator winding 92, FIG. 14, a tooth is alwayspositioned in the center of a stator pole; in FIG. 14A there arepositioned the teeth 111, 112, 113 and 114.

In accordance with a feature of the invention, the "center tooth" isgiven a position of symmetry, by having a like magnetically activewinding section, located at each side thereof. "Like", in this context,shall means that when d-c flows through the sensor winding, the samecurrent direction is present on both sides of the tooth. Thus, even inthis case, the sensor winding is not transformer coupled with theindividual stator windings. The angle indications to the FIGS. 14C and14D refer, as in the preceding, to the angles given for the main polesas they are shown in FIGS. 9 and 10.

FIG. 14C shows a sensor winding 115 for decoupling of the secondharmonic. As can be easily recognized, starting from a terminal 116, thewinding is first led to the right wave winding with a winding pitch of180° electrical: L=90° in such manner as to be positioned in each caseto the right of the center teeth 111 to 114. The winding direction isreversed at the end, and the winding 115 is returned again to the rightto a terminal 117, but now is positioned to the left of the center teeth111 to 114, that is, shifted by one slot partition. Thus, on both sidesof the center teeth there are positioned like magnetically active coilsections, that is, in the coil sections situated at both sides of onecenter tooth, a voltage of the same direction is induced duringoperation. Such an arrangement is again electrically symmetricallyrelative to the stator winding 92 so that no transformer couplingoccurs.

The arrangement of a sensor winding for coupling-out of a fourthharmonic in the winding construction of FIG. 14B is more difficult. Sucha sensor winding requires a coil step of 180° electrical: 4=45°electrical, and since the slots 89 have a distance of 30° electrical, amagnetically active section of the sensor winding would have to besituated on a tooth end.

FIG. 14D shows the solution of this problem in accordance with theinvention by providing a sensor winding 118 for the coupling-out of thefourth harmonic. This winding starts at a terminal 121 and runs fromthere towards the left, and in particular alternating with winding stepsof 30° and 60° electrical, such that in each case a magnetically activesection is situated to the left of the four center teeth 111 to 114.After passing through all slots, the winding direction is reversed andthe wave winding runs again with alternation 30°-- and 60°-- stepsthrough the slots toward the right to the connector 122, as shown,however shifted by a slot partitiion such that now the magneticallyactive sections are situated to the right of the center teeth 111 to114. Like winding sections of both wave windings are situated forexample jointly in the slots 94 and 97, and similarly like windingsections are situated on both sides of the middle teeth, that is, forexample on both sides of the center tooth 111 in the slots 95 and 96. Inother words: all 24 slots are at least covered once, and a third of themare covered twice. The angular distance of the doubly covered slots tothe next two winding sections of opposite direction also amounts to 30°electrical and 60° electrical, that is, on the average 45° electrical,as is shown in FIG. 14D for the slot 97. This average distancecorresponds to the fourth harmonic to be obtained. The angular distancesof 60° and 30° electrical also present correspond to the third and sixthharmonic, which, according to FIG. 15 practically are both equal to zeroand therefor do not interfere.

A doubled number of stator slots allows to couple-out the fourth andeight harmonic in analogy to FIGS. 14C and 14D. With respect to FIGS.14C and 14D, all the pitch values would have to be halved. In otherwords, FIG. 14C and 14D would have to shrink to half width underconsideration of the symmetry relative to the center teeth in order toavoid transformer coupling. Naturally, in accordance with the sameprinciple, sensor windings can be constructed for other slot numbers andother harmonics. The position of the galvanomagnetic sensor 16 betweentwo main windings is also shown in the FIGS. 5 and 14B.

FIGS. 6 to 8 and 11 to 13 show possible constructions of sensor windingsfor a four pole axial air gap, or flat motor. Its rotor shown in FIG. 8of the German Patent Disclosure Document DE-OS No. 27 30 142 and itsmain winding correspond to the winding shown in FIG. 9 of said PatentDisclosure Document No. 27 30 142. It comprises four approximatelysector shaped flat coils 101 to 104, which are positioned around a shaft100 with equal angular distances of 180° electrical (=90° mechanical)each. The Hall-generator 16 is disposed on the bisecting line of theangle between the coils 102 and 103. The connectors of the four coilsare designated in analogy to FIG. 4 with 49,50 and 51, 52, respectively.The circuit corresponds to the circuit of FIG. 4.

FIGS. 6 to 8 show sensor windings for coupling-out of the secondharmonic. In FIG. 6, the magnetically active sections 105 of the sensorwinding, which is herein designated as 106 (this number is thereforeindicated in parentheses in FIG. 4), are located in each case on thebisecting line of the angle between the main windings 101 to 104 and ontheir center axes. A wave or meander shaped winding is thus obtained,and its terminals are designated in FIG. 6 as 107 and 108. The meandercan be passed several times for increasing the voltage. It is importantthat the magnetically active sections 105 extend over the full width ofthe rotor magnet, which is indicated in FIG. 6 by dot-dash lines. Themagnetically active sections 105 have in each case a distance from eachother of 90° electrical in order to pick up only the second harmonic.The sensor winding 106 of FIG. 6 is suitable for axial air gap motorshaving no stray field in the direction of shaft 100. Thus, the sensorwinding 106 is not transformer coupled to the main windings 101 to 104.

In case a stray flux occurs in the direction of the shaft 100, thesensor windings 106' and according to FIG. 7 and 106", according to FIG.8, respectively, can be employed. The basic form according to FIG. 6 isemployed in both cases, but in FIG. 7 the winding is looped back on thesame path resulting in a doubling of the starting voltage. Thisarrangement also corresponds to that of FIG. 3C. In FIG. 8 the returnpath 110 runs around the shaft 100, but no longer across the rotor 109,that is, the latter does not induce any voltages in the return path 110upon rotation by the stray flux parallel to the direction of the shaft.In FIG. 7 as well as in FIG. 8, the voltages which are induced in thecorresponding sensor winding by the stray flux in shaft direction canceleach other. The return path 110 can also be disposed within the meanderwinding. In FIGS. 6 to 8 the sensor windings can be provided as aprinted circuit on a thin foil and can be mounted in this form on thestator transformer-decoupled and in proper position.

FIGS. 11 and 12 show, for the same four pole motor according to FIG. 6,sensor windings for coupling-out of the fourth harmonic, that is, with apitch of 45° electrical=22.5° mechanical between the magnetically activesections as is shown in FIGS. 11 and 12.

In FIG. 11 the sensor winding is designated as 124 and its terminals aremarked 125, 126. The construction corresponds completely to that of FIG.7, that is, the wave winding is looped back again on the same path tothe exit.

In FIG. 12 the sensor winding is designated as 127 and its terminals aremarked 128 and 129. The construction entirely corresponds to that ofFIG. 8, that is a return path 130 is here looped back around the fullshaft 100. In order to clarify the orientation relative to the mainwindings 101 to 104 according to FIG. 6, there, and in FIGS. 11 to 13, adash-dot reference line 133 is drawn, running in all four figuresthrough a magnetically active section of the corresponding sensorwinding, and representing the bisecting line of the angle between thestator windings 101 and 103.

FIG. 13 shows the sensor winding 135 printed on an insulating foil 134.The magnetically active sections of the sensor winding 135 have anangular distance of 180° electrical: 15=12° electrical and are thussuitable for decoupling of the 15th harmonic or for a sixty poletacho-magnet. A return 136 here again loops around the shaft--notshown--in order to substantially compensate for axial stray fluxes. Theterminals of the winding 135 are designated as 137 and 138. Inaccordance with FIG. 15, the coupling-out of the 15th harmonic is lessadvantageous than for example the coupling-out of the 11th or 14thharmonic, which both have considerably larger amplitudes. By anappropriate selection of the angle between the magnetically activesections, such a coupling-out can easily be provided for. For the 11thharmonic the angle between two magnetically active section would be forexample 180° electrical: 11.

FIG. 15 shows the frequency spectrum of the voltage shown in FIG. 10B.The amplitude μ of the voltage shown in FIG. 10 is normalized to be100%. It can be recognized that the fundamental of this voltage has anamplitude of about 87.8% of μ, that the second harmonic is about halfthe value of μ, that the fifth harmonic is about 1/5 and the eighthharmonic about 1/8 of μ. FIG. 15 is valid for a voltage with steepslopes. When the slopes are less steep, the harmonics beginning with thefifth harmonic have only very small amplitudes. Depending on the shapeof the preferably trapezoidal magnetization of the rotor, there is anupper limit of the ordinal number of the harmonics which still can beemployed when a sensor winding is desired with a reasonable number ofturns.

The sensor windings according to FIGS. 11, 12 or 13 (especially FIG.11), based on their compensation of stray fields independent of theirorigin from either the motor or the apparatus, are useful in connectionwith especially sensitive and fast control circuits (for example phaseregulators, such as phase locked loop (PLL) circuits, which generallyuse a quartz standard). Such sensor windings practically do not enlargethe motor and therefore result in very compact motors. The invention canalso be employed in this manner in motors having a rotor magnet fielddeviating considerably from a sinusoidal shape and which can be analyzedby analogy to FIGS. 10C to 10E with respect to special harmonic wavefields of different frequencies and amplitudes. This is illustrated inthe following by way of additional examples of embodiments. For suchother or non-sinusoidal fields, other forms of magnetization willresult, as will be described below with reference to FIG. 18B or 20B.

For the same or equally active parts the same reference numerals areused as in the previous figures. For purposes of unification ofnomenclature, terminology is employed as is defined in the article ofthe inventor "Two pulse brushless d-c motors" in the Journal "Asr-digestfur angewandte Antriebstechnik" Volume 1-2, 1977. FIGS. 21 and 22 of thepresent application correspond to FIG. 4 and FIG. 5 of that article andreference is made thereto for further illustration.

Definitions: The pole number always refers to the pole number 2p of therotor. For example, the motors according to FIG. 16 and FIG. 19 are fourpole, and those according to FIGS. 17, 18 and 20 are two pole motors.The invention is of course also useful for higher pole numbers. However,with increasing numbers of poles the distance between the magneticallyactive sections of the sensor winding decreases more and more.

The strand number refers to the number of separate windings of thestator and could also be designated as phase number. For example, FIGS.16, 17, 20 and 21 show three strand motors, since the stator winding ineach case comprises three separate strands, and FIGS. 18, 19 and 22 showtwo strand motors.

The pulse number indicates how many current pulses for the stator ordrive power winding are provided for a revolution of 360° electrical.For example, in FIG. 16 upon a rotation of 360° electrical, that is, ahalf turn of the rotor, each of the three strands receives a currentpulse when the circuit of FIG. 21 is employed, that is, three pulses areprovided. FIG. 16 thus shows a three pulse, four pole motor. FIG. 17 andFIG. 20 also show three pulse motors. Upon a rotation of 360° electricalin FIG. 18, which here is a full rotor turn or revolution, two currentpulses are fed to each of both stator windings by the circuit of FIG.22, that is four current pulses. The motor is a four current pulsemotor; the motor according to FIG. 19 is also four pulse.

Both three and four pulse motors generate an electromagnetic drivetorque in all rotor positions, that is, such motors can start from anygiven rotational position. The higher the pulse number, the lower thetorque variations upon rotation of the motor.

The magnetization of the rotor in FIGS. 16 to 19 has always about thesame form, as is shown by way of example in FIG. 18B, that is abouttrapezoidal. In FIG. 20 the magnetization (FIG. 20B) of the rotor (FIG.20C) is, about rectangular, that is it shows very steep slopes. Theexternal rotor is in all cases constructed identically to that ofexternal rotor 11 of FIG. 1. The rotor magnet is shown in each case indeveloped representation in FIGS. 16B, 17B, 18C, 19B and 20C.

The representation of the windings in the FIGS. 16 to 20 isconventional. In each case the slots of the sheet metal stamping arenumbered, for example in FIG. 16A from 1' to 24', and these slots arethen represented again, developed for example between FIGS. 16C and 16D,showing the exact relation to the developed windings. It can be clearlyrecognized which windings are disposed in which slot and how thesewindings are connected. Current direction is conventionally shown: a dotindicates that the current flows out of the plane of the figure and across that the current flows into the plane. The direction isarbitrarily fixed in the developed representations. The sensor windingof course has alternating current flowing therein during operation andnot a d-c.

The Hall-generators and other sensors are shown in each case in theirposition in the sheet metal stamping and in the developedrepresentation. Their designation agrees with the designation in FIGS.21 and 22, respectively. The same sheet metal stamping 88 employed inFIG. 16 as is in FIG. 2; 24 slots 89 are provided, which are designatedsequentially from 1' to 24'. A short pitch three strand main or drivepower or armature winding 130 is provided, and its three strands aredesignated as 131, 132 and 133. The three Hall-generators controllingthese strands are disposed as follows:

Hall-generator 134 is disposed between slots 6' and 7' and controlsstrand 131,

Hall-generator 135 is disposed between slot 10' and 11' and controlsstrand 132,

Hall-generator 136 is disposed between slot 14' and 15' and controlsstrand 133.

The sensor winding 137 (FIG. 16D) covers the third harmonic and hastherefore between its magnetically active sections a distance alpha of180° electrical: L=60° electrical, that is, in FIG. 16D 30° mechanical,since the rotor is four pole. The sensor winding 137 comprises two wavewindings, that is, one wave winding 139 running from the connector orterminal 138 towards the right, and one wave winding 141 running towardsthe left, or backward to the other terminal or connector 140 which isshifted with respect to the wave winding 139 by an angle beta in space,wherein beta=90° electrical/L (=90° electrical/: 3=30° electrical;L=ordinal number of the harmonic wave to be covered).

The phase position relative to the main winding 130 is selected such asto exclude transformer coupling with the main winding. The main winding131 starts in the slot 1', the main winding 132 in the slot 3', and themain winding 133 in the slot 5'. The sensor winding 137 runs fromconnector 138 to the slot 2', then back through the slot 3', thenthrough the slots 5', 7', 9', . . . 23' to slot 1' and from there backto slot 24' and then to slot 22',20', . . . 6', 4' to the connector 140.

The shape of the voltage u_(T) induced in the sensor winding 137 isshown in FIG. 16E. Obviously, this voltage comprises harmonics, however,the distance of the zero crossover passages is very uniform andtherefore this voltage is very suitable for control purposes. Therefore,FIG. 16 represents the most preferred mode of the invention.

If with the sheet metal stamping a full pitch, three strand main windingis employed, the sensor winding cannot be positioned in the slots 89without being transformer-coupled with the main winding. A solutionsuitable for this case is shown in FIG. 17, wherein the sensor windingagain is employed for (FIG. 17D) obtaining or coupling-out of the thirdharmonic. The sheet metal stamping 145 according to FIG. 17A is providedwith six symmetrically distributed, salient T-poles 146 with aconcentrated full pitch, three strand main winding 147, the threestrands of which are designated as 148, 149 and 150. The individualstrands are positioned diametrically, that is, in the main slots A-G;C-J; E-L.

Slots B, D, F, H, K and M are provided for the sensor winding 146 withthe stator poles. The sensor winding 146 is a wave-winding. It runs fromthe slot B with a winding pitch of 180° electrical a/e, i.e. L=60°electrical toward the right until slot B, and from there in the same waybackward to the slot D. The form of the voltage induced in the sensorwinding 153 during operation can be recognized from FIG. 17E. The threeHall-generators or other equivalent sensors are disposed as follows:

Hall-generator 34 is disposed at slot A and controls strand 148.

Hall-generator 135 is disposed at slot E and controls strand 150.

Hall-generator 136 is disposed at slot J and controls strand 149.

The control circuit is shown in FIG. 21. Transformer coupling betweenthe sensor and the main windings can also be avoided in two-strandedwinding strands shifted 90°-electrical. This is shown in FIGS. 18 and19. FIG. 18 shows a two pole, two strand motor with a full pitch mainwinding 159 (FIG. 18E) inserted in a sheet metal stamping 160 with foursymmetrical salient T-poles 161, that is, in the four main slots A, C, Eand G. The two strands of the main winding 159 are designated as 162 and163 and wound across the motor diameter as indicated in FIG. 18A. TwoHall-generators 164, 165 are provided in a relatively shifted positionof 90° electrical, of which the one is situated at the slot C andcontrols the strand 163, whereas the other is situated at slot E andcontrols the strand 162.

Four auxiliary slots B, D, F and H are provided for receiving the sensorwinding 166. Starting at slot A clockwise, then B is spaced from A by60° and D from A by 120°. Starting at slot A counterclockwise, then H isspaced from A by 60° and F from A by 120° as is clearly shown in FIG.18A.

Starting with a terminal 167, the sensor winding 166 runs initiallythrough slot A, then the slots B, D, F and H, and returns to slot A.There the winding direction reverses back to slot H, and further to theslots D and B, and to the second connector 168. Thus the winding step is180° electrical: L, that is, 60° electrical. However, in the center ofthe developed representation in each case two winding steps have beenleft out, that is, two winding steps for each pair of poles p, in orderto avoid transformer coupling between the main winding 159 and thesensor winding 166. Correspondingly, in a four pole motor, two times twowinding steps would have to be left out, and, subsequently, a rotationsymmetrical winding is obtained providing the foregoing advantages,since thereby partition errors of the rotor magnet are bettercompensated. The corresponding circuit for four pulse operation is shownin FIG. 22. The shape of the tacho-voltage u_(T) at the sensor winding166 is shown in FIG. 19E. This voltage varies corresponding to thefundamental of the magnetization of the rotor magnet; however, thedistances of the zero passages are relatively uniform and can thereforebe used for control purposes.

If it is desired to use a conventional sheet metal stamping, for examplethe sheet metal stamping 88 according to FIG. 2 with 24 slots 89, alsofor a two stranded, four pulse motor, then, according to the invention,a sensor winding can be provided for coupling-out of the third harmonic,by spacial phase shifting of part of the sensor winding by 30°electrical (with reference to the pole distribution of the rotor magnet)versus the other part, and by additional omission of some winding slots.The transformer coupling can be avoided relative to both strands of themain winding. Such a motor is shown in FIG. 19. The sheet metal stamping88 has 24 slots 89 which are designated as 1' to 24' as in FIG. 16. Therotor uses four poles (compare FIG. 19B), and the main winding has twostrands 172, 173. The Hall-generator 164 is located between the slots12' and 13' and controls the strand 172. The Hall-generator 165 islocated between the slots 15' and 16' controls the strand 173. Thedistance between the two Hall-generators 164 and 165 thus is 90°electrical=45° mechanical. The course of the main winding 171 is shownin FIGS. 19A and 19C. The main winding 171 is 5/6 short-pitched. FIG.19D shows the position of the sensor winding 175. Starting with aterminal 176, winding 175 extends through the slots 4', 7', 9', 11',16', 19', 21' to the slot 23', and from there back again through theslots 21', 18', 16', 14', 9', 6', 4' and 1' to the other connector 177.Like the sensor winding 166, the sensor winding 175 is also mirrorsymmetrical and also leaves out two slots in each case. Furthermore, thesensor winding 175 comprises four sections 178, 179, 180 and 181, whichare shifted against each other. In each of the four sections the samepitch of 180° electrical/L=60° electrical is employed, for example, fromslot 2' to slot 4', and from slot 4' to slot 6'. The sections 178 and180 are in phase, as are the sections 179 and 181. The section 178 isshifted in phase compared to the sections 179 and 181 by an angle gammaof 90° electrical: L=30° electrical, and the same holds for the section180. Through this move and the omission of the center winding loops, itis--surprisingly--possible to avoid, also in this case, transformercoupling with both strands of the main winding 171. FIG. 19E shows theshape of the voltage u_(T) at the sensor winding 175. The voltagecomprises a small part of the fundamental wave of the rotor magnet. Theninth harmonic, with a rotor magnet (FIG. 20C) having an approximatelyrectangular magnetization as shown in FIG. 20 is illustrated in FIG. 20,collectively. FIG. 20B shows the induction curve in the direction ofrotation, and measured over the circumference of the rotor. The sensorwinding 185 has to have a sensor pitch corresponding to a ninth of thepitch of the main winding 186, that is, only about 20° electrical. In asmall or tiny motor, in general, the slot number of 9×2p required forthis cannot be used for the main winding. Thus, according to theinvention a stator arrangement with salient poles 187 and a concentratedmain winding 186 is more suitable. The winding 186 is short-pitched andis disposed in three main slots A, G and N. The three strands of themain winding 186 are designated as 188, 189 and 190. In addition, 15auxiliary slots B-F, J-M and O-S are provided having, in each case, adistance from each other of 20° electrical=20° mechanical and from themain slots A, G and N, compare FIG. 20A.

The Hall-generators 134 to 136 are arranged as follows:

The Hall-generator 134 is disposed between the slots H and J andcontrols the strand 188.

The Hall-generator 135 is disposed between the slots O and P andcontrols the strand 189.

The Hall-generator 136 is disposed between the slots B and C andcontrols the strand 190.

This is shown in FIG. 20 symbolically.

The sensor winding 185 is constructed as a wave winding. It starts atterminal 193, continues to the slot A and from there further through allslots B, C, etc. until it returns to slot A and turns there and returnsvia all slots S, R, Q, etc. to slot B, and to the other connector 194.No coupling between the sensor winding 185 and the main winding 186occurs--compare FIGS. 20D and 20E. At the terminals 193 and 194 afrequency is obtained which is nine times higher than the frequencyavailable at the Hall-generators 134 to 136 and therefore provides forgood speed control.

FIG. 21 shows schematically the permanent magnetic rotor 195 of a threepulse motor having three winding strands connected as a star anddesignated as S1 to S3. The star point 196 is connected to the positivevoltage U_(B). Three npn-transistors 197, 198, 199 are provided forfeeding these three strands. In each case the transistors are connectedwith their collector to the corresponding strand and with their emitterto the negative line 200, that is, ground. The Hall-generator 134controls the transistor 197, the Hall-generator 135 the transistor 198and the Hall-generator 136 the transistor 199. This control is onlyrepresented schematically: Normally, the control is provided by drivertransistors. In FIG. 16, for example, the strands S1 to S3 wouldcorrespond to the strands 131 to 133; in FIG. 17, the strands 148 to150; and in FIG. 20, the strands 188 to 190. During each revolution ofthe rotor 195 of 360° electrical, each of the three strands S1 to S3successively receives a current pulse, that is, in total three pulsesand the operation is three pulse. A torque is generated since the threecurrent pulses mutually overlap.

FIG. 22 shows, schematically, the rotor 203 of a four pulse motor havingtwo strands designated as S4 and S5 and connected with their star pointto ground (0 volt). The other connection of the strand S4 is to theemitter of an npn-transistor 205 and the collector of an npn-transistor206. In the same way, the other connection of the strand S5 is connectedto the emitter of an npn-transistor 207 and to the collector of annpn-transistor 208. The collectors of the transistors 205 and 207 areconnected to the positive voltage +U_(B), and the emitters of thetransistors 206 and 208 are connected to a negative voltage -U_(B). Forexample, when the transistor 206 is conducting, a current flows in theother direction through S4, and when the transistor 206 is conducting, acurrent flows in the other direction through S4. Because of the symmetryof the circuit, the same holds for S5 and the two transistors 207 and208. A control device 210 provides control of the two transistors 205 to208. Rotor position signals are fed to the control device 210 from thetwo Hall-generators 164 and 165. The transistors 205, 207, 206 and 208are successively excited, resulting in a rotating field driving therotor 203. In FIG. 18 the strands S4 and S5 correspond to the strands162 and 163, in FIG. 19 the strands 172 and 173. The present inventionpermits to obtaining, with very simple means, a measuring voltage with ahigh frequency relative to the speed of rotation of the motor andfrequency of operation pulses, and with a relatively uniform period ofduration as is required especially for speed control employing frequencyas a measure of the speed of rotation. The sensor winding which is usedas a high pass filter, and should preferably extend over 360° electricalor an integer multiple thereof mathematically n·360°-el in which n=1, 2,. . . in order to minimize partition errors, for example, from anunequal distribution of the slots or a nonuniform magnetization of therotor, and in order to obtain a very uniform operation. Interferencefrom axial stray fields in axial air gap motors can be eliminated.

I claim:
 1. Brushless d-c motor havinga permanent magnet rotor, thepoles of which have a non-sinusoidal magnetization, separated by polegaps; a stator, and an armature winding located in the stator; means forpulse energizing the armature winding; and a sensor winding positionedon the stator adjacent the armature to provide output signals induced inthe sensor winding upon operation of the motor, representative of rotorposition with respect to the sensor winding, wherein the sensor windingincludes a first portion having a first winding angle of 180°-el/L,wherein L is the ordinal of a harmonic to be obtained from the sensorwinding, and then a second portion having the same average winding anglebut wound in reverse direction to compensate for stray fields permeatingthe sensor winding, said sensor winding being positioned on the armatureto provide output signals which are a harmonic or multiple of the basefrequency induced in stationary conductors located on the stator uponrotation of the motor; and wherein the sensor winding has a windingpitch which is different from the pitch of the armature winding andcomprises magnetically active portions which are located essentiallyintermediate neighboring magnetically active portions of the armaturewinding to avoid transformer coupling between the armature winding andthe sensor winding.
 2. Brushless d-c motor comprisinga permanent magnetrotor, the poles of which have at least an approximately trapezoidal orrectangular magnetization, separated by pole gaps; a stator having aslotted core with teeth and slots circumferentially distributedthereover, and an armature winding located in the slots of the stator;an essentially cylindrical air gap separating the rotor and the stator;means for pulse energizing the armature winding; and a sensor winding,placed in slots of the stator and positioned, successively, in the samedirection in a preset number of times, with an average distance of180°-el/L between two neighboring winding sections wherein L is theordinal of the harmonic to be obtained from the sensor winding, saidsensor winding being positioned adjacent the armature to provide outputsignals induced in the sensor winding upon rotation of the motor,representative of the rotor with respect to the sensor winding, andproviding output signals which are a harmonic or multiple of the basefrequency induced in stationary conductors located on the stator uponrotation of the motor; wherein the sensor winding is a wave winding; andwherein, to avoid transformer coupling between the armature winding andthe sensor winding, said sensor winding has a winding pitch which isdifferent from the pitch of the slots and includes magnetically activeportions (FIG. 17A: 153; FIG. 20A: 185, D, K, Q) positioned in slots(FIG. 17A: B, D, F, H, K, M; FIG. 20A: D, K, Q) which are locatedessentially intermediate two neighboring slots in which filaments of thearmature winding are located.
 3. Motor according to claim 1, wherein themotor is an axial air gap motor.
 4. Motor according to claim 1, whereinthe motor is an axial air gap motor and both said first portion and saidsecond portion of the sensor winding (106', 124) comprise a wavewinding.
 5. Motor according to claim 1, wherein the motor is anessentially cylindrical air gap motor.
 6. Motor according to claim 1,wherein said armature winding comprises a multi-strand or multi-filamentwinding.
 7. Motor according to claim 1, wherein said armature windingcomprises a two-strand or two-filament winding.
 8. Motor according toclaim 1, wherein (FIG. 9) the rotor has two pole divisions including,within 300°-el, a first monopole zone of about 120°-el of one polarity,a second monopole zone of about 120°-el opposite polarity, and anangular range of about 120°-el of dipole zones of essentially equal andopposite magnetic lux, to induce substantially zero voltage in aconductor extending over the full width of the rotor upon operation ofthe motor,and wherein the sensor winding is positioned to be responsiveto the second, fourth or eighth harmonic.
 9. Motor according to claim 1,wherein said stator is a coreless stator, and said armature winding is acoreless armature winding.
 10. Motor according to claim 2 wherein thesensor winding has a forwardly--in the direction of rotation of themotor--wound portion and a reverse wound portion;and wherein the reversewound portion of the sensor wave winding is spacially shifted relativeto the forward portion.
 11. Motor according to claim 10 wherein theforward portion and the backward portion are spatially shifted withrespect to each other by an angle of 90°-el/Lwherein L is the ordinalnumber of the harmonic to be obtained from the sensor winding. 12.Brushless d-c motor comprisinga stator having a slotted core with teethand slots circumferentially distributed thereover, and an armaturewinding located on the stator; a permanent magnet rotor having anon-sinusoidal magnetization (FIG. 18B; FIG. 20A); an essentiallycylindrical air gap separating the rotor and the stator; a sensorwinding (FIG. 17D; FIG. 20D) located on the stator and havingmagnetically active portions (153, 185) with an average distance of 180°el./L between two neighboring magnetically active portions, wherein L isthe ordinal of the harmonic to be sensed by the sensor winding, to sensesaid L-th harmonic (FIG. 17E) of voltage induced by the rotor, when themotor is in operation, wherein the stator winding is a multi-filamentwinding (148, 149, 150; 188, 189, 190) located in the slots (FIG. 17A:A, C, E, G, J, L; FIG. 20A: A, G, N) of the stator core and wherein, toavoid transformer coupling between the armature winding and the sensorwinding, said sensor winding has a winding pitch which is different fromthe pitch of the slots and includes magnetically active portions (FIG.17A: 153; FIG. 20A: 185, D, K, Q) aligned with slots (FIG. 17A: B, D, F,H, K, M; FIG. 20A: D, K, Q) which are located essentially intermediatetwo neighboring slots in which filaments of the armature winding arelocated.
 13. Motor according to claim 12, wherein said multi-filamentstator winding is a three-filament winding, located in 3n slots of thestator, wherein n=1, 2, 3 . . . .
 14. Motor according to claim 12, incombination with a speed control circuit,said speed control circuithaving pulse generating means connected to the pulse energization meansof the armature winding; and an actual speed signal input meansconnected to said sensor winding and responsive to the particularharmonic of said base frequency.
 15. Motor according to claim 12,wherein (FIG. 9) the rotor has two pole divisions including, within300°-el, a first monopole zone of about 120°-el of one polarity, asecond monopole zone of about 120°-el opposite polarity, and an angularrange of about 120°-el of dipole zones of essentially equal and oppositemagnetic flux, to induce substantially zero voltage in a conductorextending over the full width of the rotor upon operation of themotor,and wherein the sensor winding is positioned to be responsive tothe second, fourth or eighth harmonic.
 16. Motor according to claim 12wherein the sensor winding is positioned relative to the armaturewinding such that the sum of the voltages which are transformer-coupledby the armature winding into the sensor winding is substantially zero.17. Motor according to claim 16 wherein the sensor winding is locatedmirror symmetrically relative to the armature winding.
 18. Motoraccording to claim 12 wherein the stator has a slotted core withintervening teeth, the core having, in the middle of the armaturewinding poles, a middle or central tooth;and wherein like magneticallyactive winding sections of the sensor winding are located in slots atboth sides of the middle tooth or central tooth.
 19. Motor according toclaim 12 wherein the armature windings have predetermined pitch;and thesensor winding is wound with non-uniform pitch to provide sensorconductors spaced circumferentially of the motor with alternatinglylarger and smaller distances, and wherein the arithmetic mean of thelarger and smaller distances between the sensor conductors correspondsat least approximately to an average sensor pitch, to permit locatingthe sensor winding on a stator which has a configuration in conflictwith a theoretically calculated sensor winding pitch to obtain thedesired harmonic.
 20. Motor according to claim 12, wherein the armaturewinding (FIG. 17D) is an essentially full-pitch winding.
 21. Motoraccording to claim 12, wherein the armature winding is a concentratedwinding (FIG. 17D, FIG. 20D).
 22. Motor according to claim 12, whereinthe sensor winding (FIG. 17D) includes three uniformly distributedmagnetically active portions (153) for each pole of the rotor to sensethe third harmonic.
 23. Motor according to claim 12, wherein the sensorwinding (FIG. 20E) includes nine uniformly distributed magneticallyactive portions (185) for each pole of the rotor to sense the ninthharmonic.
 24. Motor according to claim 12, wherein the stator hassalient poles;and auxiliary slots are formed in the salient poles, thesensor windings being located in said auxiliary slots.
 25. Motoraccording to claim 24, wherein the number of salient stator poles isgreater than the number of the rotor poles.
 26. Motor according to claim12, wherein the magnetization of the rotor is essentially trapeze-shaped(FIG. 17B, FIG. 18B);and sequential rotor poles are magnetized over adistance of approximately 180°-el in similar shape and manner ofmagnetization with respectively reverse direction of the magnetic fieldor polarity.
 27. Motor according to claim 12, wherein the magnetizationof the rotor is approximately rectangular (FIG. 20B, FIG. 20C);and inwhich sequential rotor poles have a length of approximately 180°-el ofessentially similar shape and form of magnetization, but withrespectively reverse polarity or direction of magnetization.
 28. Motoraccording to claim 12, wherein the sensor winding is a single-phasewinding.
 29. Motor according to claim 12, wherein the sensor windingextends over n×360°-el, in which n=1, 2 . . . .